J-Aggregation of an anionic oxacarbocyanine in electrostatically self-assembled multilayers

Unlike in water solution, interaction of the anionic oxacarbocyanine E (structure in Fig. 1) with three polycations electrostatically adsorbed on a quartz substrate results in an extensive J aggregation of the dye. J-aggregates grow on the film surface beyond charge saturation, making possible the formation of alternately adsorbed polycation/E multilayers. UV-visible absorption and fluorescence spectra have revealed that, although less ordered than in solution, J aggregates are dominant in dry films. They are characterized by some heterogeneity and exhibit a reorganization dynamics in the presence of water. Polarized absorption has shown that the J-band transition-dipole moments lie preferentially parallel to the film plane, thus suggesting a plausible arrangement for a bidimensional brickwork aggregate. An exploration of the effects of various preparation variables (solution concentrations and ionic strengths, dipping times, film drying speed, polycation nature and molecular weight) has afforded some insight into the processes involved in polycation/J-aggregate multilayer formation.